The prevention of lowered contrast and lowered visibility caused by external light reflection or image reflection is required of image display devices, for example, cathode-ray tube display devices (CRTs), plasma displays (PDPs), electroluminescent displays (ELDs), or liquid crystal displays (LCDs). Accordingly, it is common practice to provide an antireflection laminate on the outermost surface of an image display device from the viewpoint of reducing image reflection or reflectance using the principle of light scattering or the principle of optical interference.
In image display devices, for example, liquid crystal displays, the use of an anti-dazzling laminate as one of antireflection laminates has hitherto been known for realizing regulating optical properties to realize excellent image displays. The anti-dazzling laminate is utilized for preventing a lowering in visibility as a result of external light reflection or image reflection within image display devices. The anti-dazzling laminate is generally realized by forming an anti-dazzling layer having a concavoconvex shape on a base material. Regarding the formation of the anti-dazzling layer having a concavoconvex shape, a method has been proposed in which a resin containing a filler such as silicon dioxide (silica) is coated onto a surface of a transparent base material (Japanese Patent Laid-Open No. 18706/1994 and Japanese Patent Laid-Open No. 302506/2003). A method has also been proposed in which a concavoconvex shape is formed by embossing treatment (Japanese Patent Laid-Open No. 341070/2004).
In recent years, a demand for a higher level of definition of panel resolution has led to a higher level of fineness of the concavoconvex shape of the anti-dazzling layer. Accordingly, a concavoconvex shape having a broad and large curve has been regarded as unsuitable for meeting a demand for higher definition in the anti-dazzling laminate having the above construction and thus have not been adopted. On the other hand, when increasing the fineness of the concavoconvex shape involved in higher definition of panel resolution can meet a demand for higher definition of the panel resolution. Regarding this technique, however, it has often been pointed out that, for example, external light is reflected from the display surface resulting in such a phenomenon that, for example, the image display surface is seen white (whitening), or lowered contrast. When the anti-dazzling laminate is used on the image display surface of notebook computers and the like, a certain level of satisfactory optical properties can be provided. When the light transmitted through the backside (backlight) or the like within a display is transmitted through the concavoconvex shape face of the anti-dazzling laminate formed on the outermost surface of the panel, however, the concavoconvex shape functions as fine lenses which disturb the displayed pixels and the like, that is, “glare” is likely to occur. This unfavorable phenomenon makes it difficult to attain the effect of the anti-dazzling laminate per se. In particular, in fact, an enhancement in panel resolution has lead to a demand for further effective prevention of this “glare.”
In order to eliminate “glare” caused by an enhancement in panel resolution, for example, a method has been adopted in which surface concavoconvexes are densely provided to enhance the sharpness and, at the same time, scattering particles different from the resin for anti-dazzling layer formation in refractive index are added to, for example, impart internal scattering effect to the anti-dazzling laminate. All of proposed methods could satisfactorily solve the problem of the “glare,” but on the other hand, they sometimes lowered the visibility of the whole image. On the other hand, in the anti-dazzling laminate, the method for reducing the “glare” in high-definition panels has been regarded as a main cause of an unfavorable phenomenon, for example, a deterioration in contrast such as clouding caused by surface whitening, internal scattering effect or the like. That is, it has been regarded that “glare prevention” and “contrast improvement” are in the relationship of tradeoff, and simultaneously meeting both the requirements is difficult. In the above methods, for example, black color reproduction including jet black feeling (glossy black color feeling: wet glossy black color) in on-screen display, contrast and the like have sometimes been poor. That is, gradation rendering of black color in a light room, particularly a black color gradation difference in low gradation, cannot be regarded without difficulties resulting in lowered sensitivity. Specifically, in some cases, black and gray colors are only recognized as a blurred and identical color-tone black color. In particular, it can be said that an anti-dazzling laminate having better anti-glare properties has a significantly lowered level of visibility.
Accordingly, at the present time, the development of an optical laminate, which can effectively prevent the glare of an image surface and can realize good black color reproduction, especially glossy black color feeling, has been desired. In particular, an optical laminate, which can be used in liquid crystal displays (LCDs) as well as in other applications such as cathode ray tube display devices (CRTs), plasma displays (PDPs), electroluminescent displays, fluorescent display tubes, and field emission-type displays, has been eagerly desired.